Differential requirements for actin during yeast and mammalian endocytosis

Key features of clathrin-mediated endocytosis have been conserved across evolution. However, endocytosis in Saccharomyces cerevisiae is completely dependent on a functional actin cytoskeleton, whereas actin appears to be less critical in mammalian cell endocytosis. We reveal that the fundamental requirement for actin in the early stages of yeast endocytosis is to provide a strong framework to support the force generation needed to direct the invaginating plasma membrane into the cell against turgor pressure. By providing osmotic support, pressure differences across the plasma membrane were removed and this reduced the requirement for actin-bundling proteins in normal endocytosis. Conversely, increased turgor pressure in specific yeast mutants correlated with a decreased rate of endocytic patch invagination

A binary interaction map between turnip mosaic virus and Arabidopsis thaliana proteomes

[EN] Viruses are obligate intracellular parasites that have co-evolved with their hosts to establish an intricate network of protein-protein interactions. Here, we followed a high-throughput yeast two-hybrid screening to identify 378 novel protein-protein interactions between turnip mosaic virus (TuMV) and its natural host Arabidopsis thaliana. We identified the RNA-dependent RNA polymerase NIb as the viral protein with the largest number of contacts, including key salicylic acid-dependent transcription regulators. We verified a subset of 25 interactions in planta by bimolecular fluorescence complementation assays. We then constructed and analyzed a network comprising 399 TuMV-A. thaliana interactions together with intravirus and intrahost connections. In particular, we found that the host proteins targeted by TuMV are enriched in different aspects of plant responses to infections, are more connected and have an increased capacity to spread information throughout the cell proteome, display higher expression levels, and have been subject to stronger purifying selection than expected by chance. The proviral or antiviral role of ten host proteins was validated by characterizing the infection dynamics in the corresponding mutant plants, supporting a proviral role for the transcriptional regulator TGA1. Comparison with similar studies with animal viruses, highlights shared fundamental features in their mode of action.We thank Francisca de la Iglesia and Paula Agudo for excellent technical assistance and the rest of the EvolSysVir lab for fruitful discussions. This work was supported by grants PID2019-103998GB-I00 and PGC2018-101410-B-I00 (Agencia Estatal de Investigacion - FEDER) to S.F.E. and G.R., respectively, and PROMETEO/2019/012 (Generalitat Valenciana) to S.F.E.Martínez, F.; Carrasco, JL.; Toft, C.; Hillung, J.; Giménez-Santamarina, S.; Yenush, L.; Rodrigo Tarrega, G.... (2023). A binary interaction map between turnip mosaic virus and Arabidopsis thaliana proteomes. Communications Biology. 6(1):1-18. https://doi.org/10.1038/s42003-023-04427-81186

Potassium Starvation in Yeast: Mechanisms of Homeostasis Revealed by Mathematical Modeling

The intrinsic ability of cells to adapt to a wide range of environmental conditions is a fundamental process required for survival. Potassium is the most abundant cation in living cells and is required for essential cellular processes, including the regulation of cell volume, pH and protein synthesis. Yeast cells can grow from low micromolar to molar potassium concentrations and utilize sophisticated control mechanisms to keep the internal potassium concentration in a viable range. We developed a mathematical model for Saccharomyces cerevisiae to explore the complex interplay between biophysical forces and molecular regulation facilitating potassium homeostasis. By using a novel inference method (“the reverse tracking algorithm”) we predicted and then verified experimentally that the main regulators under conditions of potassium starvation are proton fluxes responding to changes of potassium concentrations. In contrast to the prevailing view, we show that regulation of the main potassium transport systems (Trk1,2 and Nha1) in the plasma membrane is not sufficient to achieve homeostasis

Involvement of the exomer complex in the polarized transport of Ena1 required for Saccharomyces cerevisiae survival against toxic cations

[EN] Exomer is an adaptor complex required for the direct transport of a selected number of cargoes from the trans-Golgi network (TGN) to the plasma membrane in Saccharomyces cerevisiae However, exomer mutants are highly sensitive to increased concentrations of alkali metal cations, a situation that remains unexplained by the lack of transport of any known cargoes. Here we identify several HAL genes that act as multicopy suppressors of this sensitivity and are connected to the reduced function of the sodium ATPase Ena1. Furthermore, we find that Ena1 is dependent on exomer function. Even though Ena1 can reach the plasma membrane independently of exomer, polarized delivery of Ena1 to the bud requires functional exomer. Moreover, exomer is required for full induction of Ena1 expression after cationic stress by facilitating the plasma membrane recruitment of the molecular machinery involved in Rim101 processing and activation of the RIM101 pathway in response to stress. Both the defective localization and the reduced levels of Ena1 contribute to the sensitivity of exomer mutants to alkali metal cations. Our work thus expands the spectrum of exomer-dependent proteins and provides a link to a more general role of exomer in TGN organization.We acknowledge Emma Keck for English language revision. We also thank members of the Translucent group, J. Arino, J. Ramos, and L. Yenush, for many useful discussions throughout this work and especially L. Yenush for her generous gift of strains and reagents. The help of O. Vincent was essential for developing the work involving RIM101. We also thank R. Valle for her technical assistance at the CR Laboratory. M. Trautwein is acknowledged for data acquisition and discussions during the early stages of the project. C.A. is supported by a USAL predoctoral fellowship. Work at the Spang laboratory was supported by the University of Basel and the Swiss National Science Foundation (31003A-141207 and 310030B-163480). C.R. was supported by grant SA073U14 from the Regional Government of Castilla y Leon and by grant BFU2013-48582-C2-1-P from the CICYT/FEDER Spanish program. J.M.M. acknowledges the financial support from Universitat Politecnica de Valencia project PAID-06-10-1496.Anton, C.; Zanolari, B.; Arcones, I.; Wang, C.; Mulet, JM.; Spang, A.; Roncero, C. (2017). Involvement of the exomer complex in the polarized transport of Ena1 required for Saccharomyces cerevisiae survival against toxic cations. Molecular Biology of the Cell. 28(25):3672-3685. https://doi.org/10.1091/mbc.E17-09-0549S367236852825Ariño, J., Ramos, J., & Sychrová, H. (2010). Alkali Metal Cation Transport and Homeostasis in Yeasts. Microbiology and Molecular Biology Reviews, 74(1), 95-120. doi:10.1128/mmbr.00042-09Bard, F., & Malhotra, V. (2006). The Formation of TGN-to-Plasma-Membrane Transport Carriers. Annual Review of Cell and Developmental Biology, 22(1), 439-455. doi:10.1146/annurev.cellbio.21.012704.133126Barfield, R. 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Three new dominant drug resistance cassettes for gene disruption inSaccharomyces cerevisiae. Yeast, 15(14), 1541-1553. doi:10.1002/(sici)1097-0061(199910)15:143.0.co;2-kHayashi, M., Fukuzawa, T., Sorimachi, H., & Maeda, T. (2005). Constitutive Activation of the pH-Responsive Rim101 Pathway in Yeast Mutants Defective in Late Steps of the MVB/ESCRT Pathway. Molecular and Cellular Biology, 25(21), 9478-9490. doi:10.1128/mcb.25.21.9478-9490.2005Herrador, A., Herranz, S., Lara, D., & Vincent, O. (2009). Recruitment of the ESCRT Machinery to a Putative Seven-Transmembrane-Domain Receptor Is Mediated by an Arrestin-Related Protein. Molecular and Cellular Biology, 30(4), 897-907. doi:10.1128/mcb.00132-09Herrador, A., Livas, D., Soletto, L., Becuwe, M., Léon, S., & Vincent, O. (2015). Casein kinase 1 controls the activation threshold of an α-arrestin by multisite phosphorylation of the interdomain hinge. Molecular Biology of the Cell, 26(11), 2128-2138. doi:10.1091/mbc.e14-11-1552Herranz, S., Rodriguez, J. M., Bussink, H.-J., Sanchez-Ferrero, J. C., Arst, H. N., Penalva, M. A., & Vincent, O. (2005). Arrestin-related proteins mediate pH signaling in fungi. Proceedings of the National Academy of Sciences, 102(34), 12141-12146. doi:10.1073/pnas.0504776102Hoya, M., Yanguas, F., Moro, S., Prescianotto-Baschong, C., Doncel, C., de León, N., … Valdivieso, M.-H. (2016). Traffic Through theTrans-Golgi Network and the Endosomal System Requires Collaboration Between Exomer and Clathrin Adaptors in Fission Yeast. Genetics, 205(2), 673-690. doi:10.1534/genetics.116.193458Huranova, M., Muruganandam, G., Weiss, M., & Spang, A. (2016). Dynamic assembly of the exomer secretory vesicle cargo adaptor subunits. EMBO reports, 17(2), 202-219. doi:10.15252/embr.201540795Kung, L. F., Pagant, S., Futai, E., D’Arcangelo, J. G., Buchanan, R., Dittmar, J. C., … Miller, E. A. (2011). Sec24p and Sec16p cooperate to regulate the GTP cycle of the COPII coat. The EMBO Journal, 31(4), 1014-1027. doi:10.1038/emboj.2011.444Lamb, T. M., & Mitchell, A. P. (2003). The Transcription Factor Rim101p Governs Ion Tolerance and Cell Differentiation by Direct Repression of the Regulatory Genes NRG1 and SMP1 in Saccharomyces cerevisiae. Molecular and Cellular Biology, 23(2), 677-686. doi:10.1128/mcb.23.2.677-686.2003Lamb, T. M., Xu, W., Diamond, A., & Mitchell, A. P. (2000). Alkaline Response Genes ofSaccharomyces cerevisiaeand Their Relationship to theRIM101Pathway. Journal of Biological Chemistry, 276(3), 1850-1856. doi:10.1074/jbc.m008381200Madrid, R., Gómez, M. J., Ramos, J., & Rodrı́guez-Navarro, A. (1998). Ectopic Potassium Uptake intrk1 trk2Mutants ofSaccharomyces cerevisiaeCorrelates with a Highly Hyperpolarized Membrane Potential. Journal of Biological Chemistry, 273(24), 14838-14844. doi:10.1074/jbc.273.24.14838Maresova, L., & Sychrova, H. (2004). Physiological characterization of Saccharomyces cerevisiae kha1 deletion mutants. Molecular Microbiology, 55(2), 588-600. doi:10.1111/j.1365-2958.2004.04410.xMarqués, M. C., Zamarbide-Forés, S., Pedelini, L., Llopis-Torregrosa, V., & Yenush, L. (2015). A functional Rim101 complex is required for proper accumulation of the Ena1 Na+-ATPase protein in response to salt stress in Saccharomyces cerevisiae. FEMS Yeast Research, 15(4). doi:10.1093/femsyr/fov017Mulet, J. M., Leube, M. P., Kron, S. J., Rios, G., Fink, G. R., & Serrano, R. (1999). A Novel Mechanism of Ion Homeostasis and Salt Tolerance in Yeast: the Hal4 and Hal5 Protein Kinases Modulate the Trk1-Trk2 Potassium Transporter. Molecular and Cellular Biology, 19(5), 3328-3337. doi:10.1128/mcb.19.5.3328Mulet, J. M., & Serrano, R. (2002). Simultaneous determination of potassium and rubidium content in yeast. Yeast, 19(15), 1295-1298. doi:10.1002/yea.909Murguía, J. R., Bellés, J. M., & Serrano, R. (1996). The YeastHAL2Nucleotidase Is anin VivoTarget of Salt Toxicity. Journal of Biological Chemistry, 271(46), 29029-29033. doi:10.1074/jbc.271.46.29029Obara, K., & Kihara, A. (2014). Signaling Events of the Rim101 Pathway Occur at the Plasma Membrane in a Ubiquitination-Dependent Manner. Molecular and Cellular Biology, 34(18), 3525-3534. doi:10.1128/mcb.00408-14Paczkowski, J. E., & Fromme, J. C. (2014). Structural Basis for Membrane Binding and Remodeling by the Exomer Secretory Vesicle Cargo Adaptor. Developmental Cell, 30(5), 610-624. doi:10.1016/j.devcel.2014.07.014Paczkowski, J. E., Richardson, B. C., & Fromme, J. C. (2015). Cargo adaptors: structures illuminate mechanisms regulating vesicle biogenesis. Trends in Cell Biology, 25(7), 408-416. doi:10.1016/j.tcb.2015.02.005Paczkowski, J. E., Richardson, B. C., Strassner, A. M., & Fromme, J. C. (2012). The exomer cargo adaptor structure reveals a novel GTPase-binding domain. The EMBO Journal, 31(21), 4191-4203. doi:10.1038/emboj.2012.268Parsons, A. B., Brost, R. L., Ding, H., Li, Z., Zhang, C., Sheikh, B., … Boone, C. (2003). Integration of chemical-genetic and genetic interaction data links bioactive compounds to cellular target pathways. Nature Biotechnology, 22(1), 62-69. doi:10.1038/nbt919Peñalva, M. A., Lucena-Agell, D., & Arst, H. N. (2014). Liaison alcaline: Pals entice non-endosomal ESCRTs to the plasma membrane for pH signaling. Current Opinion in Microbiology, 22, 49-59. doi:10.1016/j.mib.2014.09.005Ríos, G., Cabedo, M., Rull, B., Yenush, L., Serrano, R., & Mulet, J. M. (2013). Role of the yeast multidrug transporter Qdr2 in cation homeostasis and the oxidative stress response. FEMS Yeast Research, 13(1), 97-106. doi:10.1111/1567-1364.12013RIOS, G., FERRANDO, A., & SERRANO, R. (1997). Mechanisms of Salt Tolerance Conferred by Overexpression of theHAL1 Gene inSaccharomyces cerevisiae. Yeast, 13(6), 515-528. doi:10.1002/(sici)1097-0061(199705)13:63.0.co;2-xRitz, A. M., Trautwein, M., Grassinger, F., & Spang, A. (2014). The Prion-like Domain in the Exomer-Dependent Cargo Pin2 Serves as a trans-Golgi Retention Motif. Cell Reports, 7(1), 249-260. doi:10.1016/j.celrep.2014.02.026Rockenbauch, U., Ritz, A. M., Sacristan, C., Roncero, C., & Spang, A. (2012). The complex interactions of Chs5p, the ChAPs, and the cargo Chs3p. Molecular Biology of the Cell, 23(22), 4402-4415. doi:10.1091/mbc.e11-12-1015Roncero, C. (2002). The genetic complexity of chitin synthesis in fungi. Current Genetics, 41(6), 367-378. doi:10.1007/s00294-002-0318-7Rothfels, K., Tanny, J. C., Molnar, E., Friesen, H., Commisso, C., & Segall, J. (2005). Components of the ESCRT Pathway, DFG16, and YGR122w Are Required for Rim101 To Act as a Corepressor with Nrg1 at the Negative Regulatory Element of the DIT1 Gene of Saccharomyces cerevisiae. Molecular and Cellular Biology, 25(15), 6772-6788. doi:10.1128/mcb.25.15.6772-6788.2005Santos, B., & Snyder, M. (1997). Targeting of Chitin Synthase 3 to Polarized Growth Sites in Yeast Requires Chs5p and Myo2p. Journal of Cell Biology, 136(1), 95-110. doi:10.1083/jcb.136.1.95Sato, M., Dhut, S., & Toda, T. (2005). New drug-resistant cassettes for gene disruption and epitope tagging inSchizosaccharomyces pombe. Yeast, 22(7), 583-591. doi:10.1002/yea.1233Schekman, R., & Orci, L. (1996). Coat Proteins and Vesicle Budding. Science, 271(5255), 1526-1533. doi:10.1126/science.271.5255.1526Sopko, R., Huang, D., Preston, N., Chua, G., Papp, B., Kafadar, K., … Andrews, B. (2006). Mapping Pathways and Phenotypes by Systematic Gene Overexpression. Molecular Cell, 21(3), 319-330. doi:10.1016/j.molcel.2005.12.011Spang, A. (2008). Membrane traffic in the secretory pathway. Cellular and Molecular Life Sciences, 65(18), 2781-2789. doi:10.1007/s00018-008-8349-yStarr, T. L., Pagant, S., Wang, C.-W., & Schekman, R. (2012). Sorting Signals That Mediate Traffic of Chitin Synthase III between the TGN/Endosomes and to the Plasma Membrane in Yeast. PLoS ONE, 7(10), e46386. doi:10.1371/journal.pone.0046386Trautwein, M., Schindler, C., Gauss, R., Dengjel, J., Hartmann, E., & Spang, A. (2006). Arf1p, Chs5p and the ChAPs are required for export of specialized cargo from the Golgi. The EMBO Journal, 25(5), 943-954. doi:10.1038/sj.emboj.7601007Trilla, J. A., Durán, A., & Roncero, C. (1999). Chs7p, a New Protein Involved in the Control of Protein Export from the Endoplasmic Reticulum that Is Specifically Engaged in the Regulation of Chitin Synthesis in Saccharomyces cerevisiae. Journal of Cell Biology, 145(6), 1153-1163. doi:10.1083/jcb.145.6.1153Valdivia, R. H., Baggott, D., Chuang, J. S., & Schekman, R. W. (2002). The Yeast Clathrin Adaptor Protein Complex 1 Is Required for the Efficient Retention of a Subset of Late Golgi Membrane Proteins. Developmental Cell, 2(3), 283-294. doi:10.1016/s1534-5807(02)00127-2Wadskog, I., Forsmark, A., Rossi, G., Konopka, C., Öyen, M., Goksör, M., … Adler, L. (2006). The Yeast Tumor Suppressor Homologue Sro7p Is Required for Targeting of the Sodium Pumping ATPase to the Cell Surface. Molecular Biology of the Cell, 17(12), 4988-5003. doi:10.1091/mbc.e05-08-0798Wang, C.-W., Hamamoto, S., Orci, L., & Schekman, R. (2006). Exomer: a coat complex for transport of select membrane proteins from the trans-Golgi network to the plasma membrane in yeast. Journal of Cell Biology, 174(7), 973-983. doi:10.1083/jcb.200605106Weiskoff, A. M., & Fromme, J. C. (2014). Distinct N-terminal regions of the exomer secretory vesicle cargo Chs3 regulate its trafficking itinerary. Frontiers in Cell and Developmental Biology, 2. doi:10.3389/fcell.2014.00047Yahara, N., Ueda, T., Sato, K., & Nakano, A. (2001). Multiple Roles of Arf1 GTPase in the Yeast Exocytic and Endocytic Pathways. 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Moonlighting Proteins Hal3 and Vhs3 Form a Heteromeric PPCDC with Ykl088w in Yeast CoA Biosynthesis

Premi a l'excel·lència investigadora. 2010Unlike most other organisms, the essential five-step Coenzyme A biosynthetic pathway has not been fully resolved in yeast. Specifically, the gene(s) encoding the phosphopantothenoylcysteine decarboxylase (PPCDC) activity still remains unidentified. Sequence homology analyses suggest three candidates, namely Ykl088w, Hal3 and Vhs3, as putative PPCDC enzymes in Saccharomyces cerevisiae. Interestingly, Hal3 and Vhs3 have been characterized as negative regulatory subunits of the Ppz1 protein phosphatase. Here we show that YKL088w does not encode a third Ppz1 regulatory subunit, and that the essential roles of Ykl088w and the Hal3/Vhs3 pair are complementary, cannot be interchanged and can be attributed to PPCDC-related functions. We demonstrate that while known eukaryotic PPCDCs are homotrimers, the active yeast enzyme is a heterotrimer which consists of Ykl088w and Hal3/Vhs3 monomers that separately provides two essential catalytic residues. Our results unveil Hal3/Vhs3 as moonlighting proteins, involved in both CoA biosynthesis and protein phosphatase regulation

Insulin and IGF1 signalling pathways in human astrocytes <i>in vitro</i> and <i>in vivo</i>; characterisation, subcellular localisation and modulation of the receptors.

Background The insulin/IGF1 signalling (IIS) pathways are involved in longevity regulation and are dysregulated in neurons in Alzheimer’s disease (AD). We previously showed downregulation in IIS gene expression in astrocytes with AD-neuropathology progression, but IIS in astrocytes remains poorly understood. We therefore examined the IIS pathway in human astrocytes and developed models to reduce IIS at the level of the insulin or the IGF1 receptor (IGF1R). Results We determined IIS was present and functional in human astrocytes by immunoblotting and showed astrocytes express the insulin receptor (IR)-B isoform of Ir. Immunocytochemistry and cell fractionation followed by western blotting revealed the phosphorylation status of insulin receptor substrate (IRS1) affects its subcellular localisation. To validate IRS1 expression patterns observed in culture, expression of key pathway components was assessed on post-mortem AD and control tissue using immunohistochemistry. Insulin signalling was impaired in cultured astrocytes by treatment with insulin + fructose and resulted in decreased IR and Akt phosphorylation (pAkt S473). A monoclonal antibody against IGF1R (MAB391) induced degradation of IGF1R receptor with an associated decrease in downstream pAkt S473. Neither treatment affected cell growth or viability as measured by MTT and Cyquant® assays or GFAP immunoreactivity. Discussion IIS is functional in astrocytes. IR-B is expressed in astrocytes which differs from the pattern in neurons, and may be important in differential susceptibility of astrocytes and neurons to insulin resistance. The variable presence of IRS1 in the nucleus, dependent on phosphorylation pattern, suggests the function of signalling molecules is not confined to cytoplasmic cascades. Down-regulation of IR and IGF1R, achieved by insulin + fructose and monoclonal antibody treatments, results in decreased downstream signalling, though the lack of effect on viability suggests that astrocytes can compensate for changes in single pathways. Changes in signalling in astrocytes, as well as in neurons, may be important in ageing and neurodegeneration

Regulation of the Na+/K+-ATPase Ena1 Expression by Calcineurin/Crz1 under High pH Stress: A Quantitative Study

[EN] Regulated expression of the Ena1 Na+-ATPase is a crucial event for adaptation to high salt and/or alkaline pH stress in the budding yeast Saccharomyces cerevisiae. ENA1 expression is under the control of diverse signaling pathways, including that mediated by the calcium-regulatable protein phosphatase calcineurin and its downstream transcription factor Crz1. We present here a quantitative study of the expression of Ena1 in response to alkalinization of the environment and we analyze the contribution of Crz1 to this response. Experimental data and mathematical models substantiate the existence of two stress-responsive Crz1-binding sites in the ENA1 promoter and estimate that the contribution of Crz1 to the early response of the ENA1 promoter is about 60%. The models suggest the existence of a second input with similar kinetics, which would be likely mediated by high pH-induced activation of the Snf1 kinase.This work was supported by grants BFU2011-30197-C3-01, BFU2014-54591-C2-1-P and EUI2009-04147 (SysMo2) to JA. (Ministry of Industry and Competitivity, Spain, and Fondo Europeo de Desarrollo Regional [FEDER]). JA is the recipient of an Ajut 2014SGR-4 award (Generalitat de Catalunya). DC was recipient of a predoctoral fellowship from the Spanish Ministry of Education. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Petrezsélyová, S.; López-Malo, M.; Canadell, D.; Roque, A.; Serra-Cardona, A.; Marques Romero, MC.; Vilaprinyó, E.... (2016). Regulation of the Na+/K+-ATPase Ena1 Expression by Calcineurin/Crz1 under High pH Stress: A Quantitative Study. PLoS ONE. 11(6):e0158424-e0158424. https://doi.org/10.1371/journal.pone.0158424Se0158424e015842411

Potassium and Sodium Transport in Yeast

[EN] As the proper maintenance of intracellular potassium and sodium concentrations is vital for cell growth, all living organisms have developed a cohort of strategies to maintain proper monovalent cation homeostasis. In the model yeast Saccharomyces cerevisiae, potassium is accumulated to relatively high concentrations and is required for many aspects of cellular function, whereas high intracellular sodium/potassium ratios are detrimental to cell growth and survival. The fact that S. cerevisiae cells can grow in the presence of a broad range of concentrations of external potassium (10 M–2.5 M) and sodium (up to 1.5 M) indicates the existence of robust mechanisms that have evolved to maintain intracellular concentrations of these cations within appropriate limits. In this review, current knowledge regarding potassium and sodium transporters and their regulation will be summarized. The cellular responses to high sodium and potassium and potassium starvation will also be discussed, as well as applications of this knowledge to diverse fields, including antifungal treatments, bioethanol production and human disease.L.Y. is funded by grant BFU2011-30197-C03-03 from the Spanish Ministry of Science and Innovation (Madrid, Spain) and EUI2009-04147 [Systems Biology of Microorganisms (SysMo2) European Research Area-Network (ERA-NET)].Yenush, L. (2016). Potassium and Sodium Transport in Yeast. Advances in Experimental Medicine and Biology. 892:187-228. https://doi.org/10.1007/978-3-319-25304-6_8S187228892Ahmed A, Sesti F, Ilan N, Shih TM, Sturley SL et al (1999) A molecular target for viral killer toxin: TOK1 potassium channels. Cell 99:283–291Albert A, Yenush L, Gil-Mascarell MR, Rodriguez PL, Patel S et al (2000) X-ray structure of yeast Hal2p, a major target of lithium and sodium toxicity, and identification of framework interactions determining cation sensitivity. 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FOXO Regulates Organ-Specific Phenotypic Plasticity In Drosophila

Phenotypic plasticity, the ability for a single genotype to generate different phenotypes in response to environmental conditions, is biologically ubiquitous, and yet almost nothing is known of the developmental mechanisms that regulate the extent of a plastic response. In particular, it is unclear why some traits or individuals are highly sensitive to an environmental variable while other traits or individuals are less so. Here we elucidate the developmental mechanisms that regulate the expression of a particularly important form of phenotypic plasticity: the effect of developmental nutrition on organ size. In all animals, developmental nutrition is signaled to growing organs via the insulin-signaling pathway. Drosophila organs differ in their size response to developmental nutrition and this reflects differences in organ-specific insulin-sensitivity. We show that this variation in insulin-sensitivity is regulated at the level of the forkhead transcription factor FOXO, a negative growth regulator that is activated when nutrition and insulin signaling are low. Individual organs appear to attenuate growth suppression in response to low nutrition through an organ-specific reduction in FOXO expression, thereby reducing their nutritional plasticity. We show that FOXO expression is necessary to maintain organ-specific differences in nutritional-plasticity and insulin-sensitivity, while organ-autonomous changes in FOXO expression are sufficient to autonomously alter an organ's nutritional-plasticity and insulin-sensitivity. These data identify a gene (FOXO) that modulates a plastic response through variation in its expression. FOXO is recognized as a key player in the response of size, immunity, and longevity to changes in developmental nutrition, stress, and oxygen levels. FOXO may therefore act as a more general regulator of plasticity. These data indicate that the extent of phenotypic plasticity may be modified by changes in the expression of genes involved in signaling environmental information to developmental processes